When to refer a patient with genu valgum (knock knees) to an orthopedic specialist?

When to Refer Genu Valgum to Orthopedic Specialist

Refer children with genu valgum to an orthopedic surgeon when: the deformity persists beyond age 7 years, intercondylar distance exceeds 8-10 cm, there is asymmetric involvement, progressive worsening occurs, or when metabolic/systemic causes are suspected. 1, 2, 3

Age-Based Referral Criteria

• Physiologic genu valgum typically peaks at age 3-4 years and resolves spontaneously by age 7 years 3
• Immediate referral is warranted if significant valgus deformity persists beyond age 7 years, as this suggests pathologic rather than physiologic etiology 3
• Children with severe deformity at any age require orthopedic evaluation, particularly if functional impairment is present 2

Clinical Measurements Requiring Referral

• Intermalleolar distance >8-10 cm when knees are touching indicates significant deformity requiring specialist assessment 1, 2
• Measure intercondylar distance at each visit to track progression; increasing measurements warrant referral 1
• Asymmetric deformity (one knee more affected than the other, or "windswept deformity") is never physiologic and requires immediate orthopedic referral 1

Red Flags for Pathologic Causes

Metabolic/Systemic Indicators

• Short stature or decreased growth velocity suggests X-linked hypophosphatemia (XLH) or other metabolic bone disease requiring urgent evaluation 1, 2, 4
• Associated findings of abnormal gait, muscle weakness, or bone pain indicate possible XLH 1, 4
• Hepatomegaly with genu valgum raises concern for glycogen storage disease type III 1, 4

Biochemical Screening Before Referral

• Order serum phosphate, alkaline phosphatase, vitamin D, parathyroid hormone, and calcium if metabolic cause suspected 1, 2, 4
• Hypophosphatemia with elevated alkaline phosphatase strongly suggests XLH and requires immediate referral to both orthopedics and metabolic bone specialist 1, 2, 4

Functional Impairment Criteria

• Pain with activity or at rest requires orthopedic evaluation regardless of age 2, 5
• Inability to perform age-appropriate activities (running, jumping, prolonged standing) warrants referral 2, 5
• Progressive joint damage and early osteoarthritis can develop in untreated pathologic genu valgum 2, 4

Radiographic Indications

• Obtain standing anteroposterior radiographs of both lower extremities (hip-knee-ankle views) when clinical measurements suggest pathologic deformity 1, 2
• Radiographic findings requiring referral include: partial fraying or irregularity of growth plates, mechanical axis deviation into Zone 2 or greater, or metaphyseal-diaphyseal angle abnormalities 1, 4, 6
• Clinical intermalleolar distance correlates poorly with radiographic severity, so radiographs are essential for accurate assessment 7

Timing of Orthopedic Evaluation

• Patients with substantial limb deformities should be evaluated by an orthopedic surgeon experienced in metabolic bone disease 1
• Evaluation should include assessment of limb length, alignment in coronal and sagittal planes, and torsional profile 1
• Surgical intervention should be considered when deformity persists despite optimized medical treatment for at least 12 months, or when symptoms interfere with function 6
• Guided growth techniques require referral at least 2-3 years before skeletal maturity (age 14 in girls, 16 in boys) to be effective 6

Common Pitfalls to Avoid

• Do not assume all genu valgum is physiologic without measuring intercondylar/intermalleolar distance and assessing for systemic signs 2, 3
• Do not delay referral in cases with metabolic indicators, as early treatment with phosphate supplementation and active vitamin D can improve bowing in conditions like XLH 1, 2, 4
• Unilateral or asymmetric deformity is never physiologic and always requires investigation 1
• Patients with severe deformity may require multidisciplinary care including physical therapy, but this should not delay orthopedic referral 1, 5